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From "Marvin Humphrey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3218) Make CFS appendable
Date Fri, 19 Aug 2011 13:36:27 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13087704#comment-13087704
] 

Marvin Humphrey commented on LUCENE-3218:
-----------------------------------------

I don't fully grok Robert's concern, but with regards to Mike's suggestion of
inlining the metadata: Why not put that file pointer at the very end of the
file?  So that the read-time sequence of actions is: seek to 8 bytes before the
end, read the file pointer, seek back to beginning of metadata.

That way you don't need to seek backwards during writing, which IIRC used to
be an issue for Hadoop.


> Make CFS appendable  
> ---------------------
>
>                 Key: LUCENE-3218
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3218
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: core/index
>    Affects Versions: 4.0
>            Reporter: Simon Willnauer
>            Assignee: Simon Willnauer
>             Fix For: 3.4, 4.0
>
>         Attachments: LUCENE-3218.patch, LUCENE-3218.patch, LUCENE-3218.patch, LUCENE-3218.patch,
LUCENE-3218_3x.patch, LUCENE-3218_test_fix.patch, LUCENE-3218_tests.patch
>
>
> Currently CFS is created once all files are written during a flush / merge. Once on disk
the files are copied into the CFS format which is basically a unnecessary for some of the
files. We can at any time write at least one file directly into the CFS which can save a reasonable
amount of IO. For instance stored fields could be written directly during indexing and during
a Codec Flush one of the written files can be appended directly. This optimization is a nice
sideeffect for lucene indexing itself but more important for DocValues and LUCENE-3216 we
could transparently pack per field files into a single file only for docvalues without changing
any code once LUCENE-3216 is resolved.

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